An example of the technologies belonging to the same technical field is recited in Patent Document 1. A stack valve having a bucket parallel movement function according to Patent Document 1 includes a dividing valve which divides a return pressure fluid from a boom cylinder into a flow toward a junction path and a flow toward a bypass path, a branched path which is branched from the junction path and connected to an unloading path, and a switching valve which is provided on the branched path and opens or closes the branched path. This stack valve of Patent Document 1 makes it possible to return the pressure fluid to the unloading path via the branched path branched from the junction path and to prevent a pressure from occurring in the branched path. By the switching valve on the branched path, the flow of the return pressure fluid from the boom cylinder to the bucket cylinder is stopped, and hence the bucket parallel movement function is suitably cancelled.